Such a light applicator for medical applications and a method for producing a diffusor attachable to a light guide is known from U.S. Pat. No. 5,978,541. The known light applicator comprises a cylindrical core which is interspersed with light scattering particles. The light scattering particles are used as scattering centers at which the light arriving through the light guide in the diffusor is scattered.
The distribution of concentration of the scattering centers along the optical axis of the light guide connectable to the diffusor, which axis is prolongated into the diffusor, is chosen in such a way that the diffusor emits light with a predetermined light distribution.
The diffusor is produced in an extrusion process in which the concentration of the scattering centers is set by mixing two suspensions with different concentrations. The concentration of the scattering centers during the extrusion process is continuously monitored for the purpose of producing a specific concentration profile and is compared with a predetermined set value.
For the determination of the set values it is proposed to assemble prototypes of the diffusor from individual parts with different concentrations. It is then possible from the plurality of prototypes to choose the one prototype whose light distribution corresponds best to the desired light distribution. The mixing process during the extrusion of the diffusor is then set in such a way that the finished diffusor then shows approximately the desired distribution of the scattering centers.
The known light applicators are generally used within the scope of photodynamic therapy for the treatment of tumors. A photosensitizer which enriches selectively in the tumor is applied in this process. After the application of the photosensitizer the tumor and the ambient healthy tissue is irradiated with light. Toxins are produced through the thus initiated photochemical processes which damage the tumor in a purposeful manner as a result of the tumor selectivity.
Since a certain concentration of the photosensitizer (although a low one) will set even in the healthy tissue, any overdosing with light may lead to undesirable tissue damage in the healthy tissue. On the other hand, the desired therapeutic success will not to be achieved in the case of under-dosage. The tolerance range for the light dose to be applied is therefore often narrow. Since the light distribution depends on the distribution of the scattering centers, a certain distribution of concentration of the scattering centers in the diffusor is necessary for a specific light distribution. In order to ensure that the required precision in the concentration of the scattering centers can be achieved, the known method for producing the diffusor requires a complex regulation for the extrusion process.